Exploration of the impact of temperature on the formation of α-lactalbumin-oleuropein complex by the application of spectroscopy methods and molecular docking

The application of carriers is a proper means of improving the transfer and increasing the bioavailability of bioactive compounds. α-lactalbumin is the second major component of whey protein nutritionally consisted of Trp, Lys and Cys residues which can be employed as nutraceutical carriers. Oleuropein is a bioactive compound with pharmaceutical and antioxidant properties which is found abundantly in olive leaves and at lower levels in olive oil. The current study was undertaken to explore the interaction of α-lactalbumin-oleuropein complex at 25, 50 and 72 ˚C at pH 7 by using fluorescent, UV and circular dichroism spectroscopy techniques together with molecular docking. The results from UV and fluorescent studies demonstrate that site and binding constant are increased as the temperature increased due to the change in conformation and rearrangement of protein structure. Moreover, circular dichroism results depicted that α-helix and β-sheet structures are decreased and increased respectively as a result of temperature increase up to 72 ˚C. Ultimately, the molecular docking findings revealed that the best binding energy for complex formation was about -6.3 kCal/mol and the best binding site was between the α-helix and β-sheet cleft. The findings give us useful information regarding the interaction of oleuropein and α-lactalbumin which can be further used to produce functional foods.